1. Field of Invention
This invention relates generally to devices for forming thermoplastic pipes, specifically to an improved pipe bender and end socket former.
2. Prior Art
Plastic pipes used in building construction often need to be bent to round corners and follow curves. Ready-made sweep elbows or ells (curved pipe sections), which serve as curved connectors, are commercially available to suit such needs. However, such prefabricated parts are expensive, need to be stocked in a great variety of tube diameters and bend angles by contractors, and are available only in a very small number of angular configurations, i.e., 30, 45, and 90 degrees. A large inventory of sweep ells ties up much capital. Therefore, contractors sometimes use templates, or flat sheets printed with a variety of curves, to bend custom pipes in the field. A heated pipe is bent by hand and matched against the desired curve on the template. However, templates can only provide a small number of curves, and manually matching pipes against the template limits accuracy. Moreover, two connector sleeves are needed to join a sweep ell with pipes at either end, which increases the cost.
Some pipe bending jigs have been designed to allow more accurate pipe forming in the field. U.S. Pat. No. 3,776,539 to Curtis et al. (1973) shows a jig with two hinged arms, each with clamps at their ends, and a protractor to show the angle of the arms. The arms are first adjusted to the desired angle, then the heated pipe is bent and placed into the clamps. Some versions of this jig cannot form more complex shapes, such as S curves, and it has no provision to prevent the pipe from kinking when bent to a small radius. As a result, the sweep elbows it produces do not conform to the National Electrical Manufacturers Association (NEMA) standard for maximum allowable deformation (internal and external diameters--ID and OD). Moreover, the resulting sweep ell still requires the use of connector sleeves.
U.S. Pat. No. 4,156,588 to Miller et al. (1979) shows a jig with two clamps slidably mounted on a rod, and protractors on each clamp to show the angle of the bend. Plugs seal the ends of the pipe to maintain internal pressure to prevent kinking. However, this jig is inconvenient because it requires the clamps to be individually adjusted for each bend radius and angle. Furthermore, the resulting sweep ell also requires the use of connector sleeves. Also, Miller's jig is designed to form bends in pipes having diameters of about 5 cm or greater.
U.S. Pat. No. 4,273,523 to Levens (1981) shows a sweep ell production device which automatically bends pipe sections by feeding the pipe section from an extruder into a curved forming sleeve. It can only be used with production pipe extruders; not in the field. Furthermore, the resulting sweep ells also require the use of connector sleeves.
In conclusion, pipe bending in the field can be difficult. Templates are limited in their scope and accuracy, while existing jigs are either limited in the shapes they can form, or very inconvenient in their use, and lack any internal pipe support so that the resultant bent pipes do not comply with the NEMA standard for permissible deformation. Furthermore, pipe sections produced by these jigs require the use of connector sleeves, which increase cost.